Re-refined waste crankcase oils and method

ABSTRACT

A method of removing contaminants, including detergents and other additives, dispersed in waste crankcase oil. A treating solution comprising a mixture of (1) compounds furnishing nitrate ions, such as nitric acid, or nitrate salts, and (2) sulfuric acid; in a ratio of about one-half to about two parts by weight of nitrate ion per part by weight of sulfuric acid, is allowed to react with waste crankcase oil, preferably waste crankcase oil which has been previously partially re-refined, in a ratio of from about 0.1 percent to about 2 percent by volume of the treating solution in relation to the volume of waste oil. The mixture may be heated to about 80* C. with thorough agitation. Improved separation is sometimes obtained by adding dimethyl formamide or dimethyl sulfoxide to the reaction mixture.

United States Patent [72] Inventor Graham L. Gulick Schiller Park, Ill. [211 App]. No. 814,845 [22] Filed Apr. 9, 1969 [45] Patented Sept. 21, 1971 73] Assignee Quvoe Chemical Industries, Inc.

Schiller Park, Ill.

[54] RE-REFINED WASTE CRANKCASE OILS AND METHOD 12 Claims, No Drawings [52] US. Cl 208/181, 208/179 [51] lnt.C1 ..C10m1l/00 [50] Field of Search 208/179, 181,177,90, 219, 220, 224, 252, 265

[56] References Cited UNITED STATES PATENTS 54,978 5/1866 Taylor 208/177 1,815,366 7/1931 Stratford. 208/177 2,952,624 9/1960 lsister et al 208/179 Primary Examiner Delbert E. Gantz Assistant Examiner-J. Nelson An0rneyGreist, Lockwood, Greenawalt & Dewey ABSTRACT: A method of removing contaminants, including detergents and other additives, dispersed in waste crankcase oil. A treating solution comprising a mixture of (1) compounds furnishing nitrate ions, such as nitric acid, or nitrate salts, and (2) sulfuric acid; in a ratio of about one-half to about two parts by weight of nitrate ion per part by weight of sulfuric acid, is allowed to react with waste crankcase oil, preferably waste crankcase oil which has been previously partially re-reflned, in a ratio of from about 0.1 percent to about 2 percent by volume of the treating solution in relation to the volume of waste oil. The mixture may be heated to about 80 C. with thorough agitation. Improved separation is sometimes obtained by adding dimethyl formamide or dimethyl sulfoxide to the reaction mixture RE-REFINED WASTE CRANKCASE OILS AND METHOD BACKGROUND OF THE INVENTION The present invention relates to the refining, or as it is sometimes known, re-refining of waste crankcase oils, or partially refined waste crankcase oils. For reasons of economy, it is preferred to utilize the process of the present invention on waste crankcase oil which has been partially refined by removal of coarser dispersed particles and water, such as by treatment as further set forth in my copending application, Ser. No. 725,940, filed May 1, 1968. This application, in brief, describes treatment of waste crankcase oil by the addition thereto of sodium hydroxide or other strong electrolyte, and a free radical generator, such as hydrogen peroxide or the like. This treatment removes a good portion of the contaminant particles which include metallic iron, and iron-containing compounds, lead compounds, as well as other contaminants, known to those skilled in the art of re-refining waste crankcase oil to be present therein. The present invention may also be practiced on partially refined waste crankcase oil produced by other methods, provided that the conditions under which partial refining take place are mild enough so that the oil phase and the suspended additives remain substantially unchanged during partial re-refining.

lt has long been known that it is possible to obtain reusable oil products from waste crankcase oil. However, the nature and composition of commercial motor oils, which, after use, form waste crankcase oil, have changed considerably in the past 5 to years, and as the production of oils which have more powerful detergent and dispersant characteristics has increased, re-refining has become more difficult. Present day automobile engine oils contain a number of such detergent and dispersant additives, so that material entering the oil which results from wear or abrasion of engine parts, airborne dirt, combustion byproducts, various crankcase condensants, and the like, can be suspended in the oil until it is drained from the crankcase at periodic intervals.

As oils have become more effective in suspending and dispersing such contaminants, the detergent systems used therein have become so effective, that the point has been reached where the detergents and other additives are so resistant to leaving the oil phase that it has become nearly impossible to separate them by physical or mechanical means, or by chemical means which have been heretofore found to be economically feasible. Accordingly, the detergents, and in some cases the contaminants suspended by the detergents, remain in the oil and very strongly resist efforts to remove them by previously known re-refining operations, except by methods which are so harsh that the additives and even a part of the oil are destroyed by conversion to an undesirable acid sludge. lt is well known in the art that there is no economical method of disposing of acid sludge, which creates a health hazard to persons as well as to wildlife of all kinds.

Typical of such contaminants are nonhydrocarbon contaminants which may include lead from fuel additives; copper from bearings; zinc from additives such as zinc dithiophosphate; iron and aluminum, formed from wear of engine parts; and still other contaminants. Many of these contaminants are objectionable because they comprise ash-forming constituents which are known to be undesirable in motor oils. However, whether or not such contaminants are ash-forming constituents and regardless of the exact chemical form in which such contaminants are present, their presence is undesirable, and these contaminants, for the purposes of the present invention, may be referred to generally under the term nonhydrocarbon contaminants.

Since it is well known that lubricating oil of the type used as a base for ordinary motor oils is chemically stable and does not break down under conditions to which it is exposed in use, it follows that such motor oil does not wear out," and suffers only from being contaminated with the contaminants referred to above. Whether these contaminants are introduced into the oil by exposure thereof to dirt, or whether the oil is diluted with raw fuel, water, or other combustion byproducts, including acids or the like, is not particularly important to the present invention. A matter which is important, however, is that the superior performance characteristics of motor oils of today is attained by the addition of various additives, including detergents, dispersants, pour point depressants, viscosity index improvers, and other valuable but highly expensive additives to such ordinary motor oil stock. It is quite common today for the additives in a quart of additive-containing motor oil to cost as much as the refined oil which comprises the remainder of the product. The exact nature of these additives, and the purposes served by the addition thereto of motor oil is an extensive and complex subject in itself, and does not form a necessary part of the present invention. However, it would be highly desirable to recover these expensive additives, either individually, or as components of a mixture in which such additives are available for further separation or reclamation for reuse in motor oils for other uses.

Accordingly, one object of the present invention is to provide a method for re-refining waste crankcase oils, particularly partially re-refined waste crankcase oils.

Another object is to provide a method of refining waste crankcase oils which is of improved effectiveness particularly in removing ash-fonning constituents and nonhydrocarbon contaminants from waste motor oil.

A still further object is to provide a method of removing contaminants from waste crankcase oil by a method utilizing relatively mild conditions in relation to prior art methods.

A still further object is to provide a method of removing detcrgents, dispersants, and the like as well as contaminants suspended thereby, from waste crankcase oil or partially rerefined waste crankcase oil.

Another object is to provide a method of re-refining waste crankcase oils in which motor oil additives will not be subjected to substantial chemical change while such additives are being separated from waste crankcase oil.

A further object is to provide a method of treating waste crankcase oils under conditions such that additives may be recovered without substantial change so as to be suited for further separation, recovery or reclamation.

Another object is to provide a method of refining a waste crankcase oil or a partially refined waste crankcase oil so that the resulting product may be distilled to form a variety of usable, contaminant-free petroleum products.

Still another object of the invention is to provide a method of re-refining waste crankcase oils which involves conditions under which no acid sludge is created.

A still further object is to provide a method of treating waste crankcase oils which includes the use of a mixed acid reagent comprising nitric and sulfuric acids mixed together before usmg.

A still further object of the invention is to provide a method of re-refining waste crankcase oil which includes treating a batch of waste crankcase oil with a treating reagent having nitrate ions and sulfuric acid therein, and subsequently treating the oil with an additional reagent such as dimethyl sulfoxide or dimethyl formamide.

Another object is to provide a method of re-refining waste crankcase oils which includes treating such oils with a nitrate ionand sulfuric acid-containing treating reagent and subsequently adding a solvent or reagent to promote removal of adsorbed air helping to suspend said contaminants in the oil, and thereby to provide an antidetergent effect on the contaminants dispersed in the oil.

Another object is to provide a re-refined crankcase oil product made by the methods described herein, and to provide recovery substantially intact of separated oil additives which may be treated for separation or reclamation, or both, by subsequent processing.

The above objects, and others which are inherent in the invention, are attained by treating a batch of waste crankcase oil, previously partially refined if possible, with a treating reagent comprising a mixture of nitrate ionand sulfuric acidcontaining material having about one'half to two parts by weight of nitrate ion for each part by weight of sulfuric acid, and being present in a ratio of about 0.1 percent to about 2 percent by volume in relation to the volume of oil to be treated, and preferably by further treating the oil with an additional compound such as dimethyl sulfoxide or dimethyl formamide, to accelerate settling of the contaminants and additives.

The exact manner in which the invention accomplishes these objects will become more apparent when the objects are considered in connection with the following description of the preferred embodiments of the invention, which are set forth by way of example in the detailed description, and are defined in the appended claim.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION The process of the present invention will now be described by reference to a number of examples which illustrate the method of the invention.

EXAMPLE 1 A suitable size batch, for example, several hundred gallons or more, of a partially re-refmed crankcase oil, preferably prepared by the method described in my copending application Ser. No. 725,940, filed May 1, 1968, is disposed in a reaction vessel. This batch of oil includes those nonhydrocarbon contaminants which are dispersed or suspended in such oil, and which have not been separated therefrom by the addition of the reagents referred to in such copending application. As pointed out above, this oil includes additives of various types, including detergents, and dispersible contaminants suspended thereby.

To this batch of oil, which may be at room temperature l5-20 C.), is added a premixed treating reagent which comprises about 70 percent by volume of 70 percent nitric acid and about 30 percent by volume of 98 percent sulfuric acid. This premixed acid treating reagent is thoroughly dispersed in the oil and brought into intimate contact therewith by a high shear mixing operation, in a known manner, carried out so as to achieve maximum mixing, but so as to avoid vortexing of the mix or entrapping of additional air therein. The mixed acid is provided in an amount equal to about 0.6 percent by volume in relation to the volume of the waste oil. Approximately 0.6 percent by volume of dimethyl sulfoxide is then added to the mix, which is then heated to a temperature of about 80 C., with continuous mixing action. When the temperature reaches about 80 C., mixing is discontinued and the mix is allowed to settle. Thereafter, about 90 percent or more by volume of the mix may be drawn off from the top of the reaction vessel, without disturbing a flocculent, somewhat waxy, semisolid phase formed at the bottom of the vessel. The oil drawn from the top of the vessel is typically a clear, medium to dark brown oil, which is neither strongly acidic nor basic, but which is normally measurably slightly acidic, but not sufficiently acidic to require further neutralization.

The resulting oil product may then be distilled under vacuum conditions, for example, one-half inch (abs) of mercury, and will typically yield a low boiling fraction which is relatively high in gasoline, or the like a light oil fraction having a somewhat higher boiling range, and a still higher boiling range fraction which comprises the lubricating oil fraction. The residue is a sulfur-free petroleum product which is typically suitable for use as a residual fuel oil or for other known uses. Typically, the lubricating oil fraction may be that portion which distills in the range of about 250 C., or more, under the vacuum conditions described, while the light oil fraction might typically be distilled at a temperature of from about 100 C. to about 210 C.

The lubricating oil thus re-refmed from the waste crankcase oil may be, if desired, subjected to known treatment to remove undesirable color, if such color is present, although in many cases, the oil resulting from the distillation is of a suitably light color for immediate use as a lubricating oil, free of the contaminants removed by the process of the invention. Known additives of any given type may then be added to this re-refined oil, for imparting desired properties thereto.

The portion of the mix from which the supernatant, rerefined oil was drawn is a phase in which the precipitated additives are concentrated, and this portion of the treated mix is suited for subsequent treatment for separation and/or reclamation of these additives; however, the methods of doing so are not within the scope of the present invention. Likewise other known methods of altering the color of the oil, produced by the method of the present invention may be used, if believed necessary, but these methods also do not form a part of the present invention.

EXAMPLE 2 The contaminants suspended in a batch of waste crankcase oil are removed in the same manner as set forth in example 1, except that the dimethyl sulfoxide is added to the mix before the mixed acid treating reagent is added. The results of this method are substantially the same as those obtained by the method of Example 1, demonstrating that it is not necessary to add the dimethyl sulfoxide in any particular order in relation to the time of the addition of the mixed acid reagent to obtain satisfactory results.

EXAMPLE 3 A separation is carried out according to the method of example l, except that the step of adding the dimethyl sulfoxide is omitted entirely from the process. The resulting products are the same, but the separation of the contaminants may take place at a slower rate, and, in some cases, the form of the precipitated contaminants may appear somewhat different to the eye. Accordingly, the addition of dimethyl sulfoxide or like reagent is preferred, but is not absolutely essential to the practice of the present invention.

EXAMPLE 4 A separation according to the method of example 1 was carried out as set forth therein, except that about 0.6 percent of dimethyl formamide, by volume, was added instead of the dimethyl sulfoxide referred to in example '1. The time of adding the dimethyl formamide in relation to the time of adding the mixed acid treating reagent was not critical. The results obtained were substantially identical to the results obtained by the method of example 1.

EXAMPLE 5 A method was carried out according to any one of the foregoing examples 1 through 4, except that the mixed acid treating reagent was added in a ratio of about 0.1 percent by volume in relation to the volume of the oil. ln the case of certain typical batches of partially re-refined waste crankcase oil, this proportion of reagent was sufficient, and excellent results were obtained in the same manner as set forth in any of the foregoing examples. In the cases where dimethyl formamide or dimethyl sulfoxide were used, these reagents were added in amounts by volume which were approximately equal to the amounts of mixed acid added. However, experimentation has shown that, since these compounds are not strictly necessary to the practice of the present invention, the proportions thereof used may vary within considerably limits in relation to the variation of proportions of the treating compounds.

EXAMPLE 6 A separation was carried out according to any of the abovedescribed examples 1 through 4, except that up to about 2 percent by volume of the mixed acid treating reagent in relation to the volume of oil were added. This method also produced successful results with representative batches of waste crankcase oil. As in example 5, the dimethyl formamide or dimethyl sulfoxide, where used, were added in an amount which was approximately equal by volume to the amount of mixed acid treating reagent used.

EXAMPLE 7 A separation was carried out in accordance with the method of example 1, except that the acids were not premixed before addition thereof to the waste oil. However, precautions were taken to make certain that a thorough mixing was obtained; the nitric acid was added to the oil with thorough and complete mixing, then the sulfuric acid was added as the mixing was continued. The results obtained were substantially the same as those obtained when the method of example l was used,

EXAMPLE 8 A separation according to the method of example 7 was carried out, except that the sulfuric acid was added to the mix before the nitric acid was added. In this case, however, the sulfuric acid was diluted from the 98 percent form to about 50 percent sulfuric acid, before addition thereof to the oil, to make certain that no charring of the additives took place, and to avoid the formation of any acid sludge. The nitric acid was then added, and results were substantially the same as those obtained by the method of example 7. Again, very thorough mixing was initiated and maintained during the entire time of addition ofthe reagents to the oil.

EXAMPLE 9 About 1,000 liters of oil prepared according to the method set forth in my copending application were placed in a reaction vessel, and about 10 kilograms of sodium nitrate (NaNO were diluted with sufficient water to make a treating composition of about liters, and added to the mix under conditions of very high shear agitation. Next, about 6 liters of 98 percent sulfuric acid were added while the high shear mixing continued. Mixing was further continued while the mix was heated to 80 C., whereupon the agitation was stopped, and the contaminants were allowed to settle as set forth in example Excellent results were obtained.

EXAMPLE 10 A separation was carried out according to example 9, except that about 10 liters of 98 percent sulfuric acid were added instead of the 6 liters of example 9. Excellent results were again obtained.

EXAMPLE 1 l A separation was carried out according to either example 9 or 10, except that about 0.01 percent in relation to the weight of the nitrate salt of a nonionic detergent (a n-nonyl polyoxethylene ethanol, for example) was added to the nitrate solution before it was added to the oil. Other conditions remained the same, and excellent results were obtained.

Experience has indicated, as pointed out above, and as further detailed herein, that the use of too much mixed acid or other nitrate ion-sulfuric acid-containing treating reagent renders the process equally less effective as does the use of too little reagent. In extreme cases, it appears that the method may actually be unsatisfactory or inoperative. Thus, the exact range of percentages of treating reagent and other materials appears to depend on certain factors which are not understood with certainty, except that, as can be seen by reference to the above examples, the treatment is effective within a fairly broad range, but is not effective at any or all concentrations of the treating reagent.

In this connection, of course, it will be understood that waste crankcase oil" as the term is used herein, and in the appended claims, is normally a complex mixture of difficult to identify components, normally having its source in a highly random mixture of oils obtained from service stations, industrial plants, transportation companies of all types, and the like. Consequently, each batch is different, as a rule, an certain batches may have a much higher percentage of oil from one given source, and may therefore have high or low concentrations of certain additives or contaminants. The waste oil may include greases, motor oils, truck oils, diesel oils, cutting oils, transmission and differential fluids, hydraulic oil, and the like, as well as any combination of them, for example. Thus, a mixture which may be treated for operation of contaminants and additives by the method of the present invention need not actually originate in a crankcase, but may originate from any of the used oil sources referred to herein or even other sources. The term waste crankcase oil," however, is used because waste crankcase oil is a typical source of such material, and the process of the invention is of particular interest to those processing waste crankcase oil.

The reasons for the success of the method of the present invention in separating various contaminants, including additives as well as material suspended or dispersed by such additives from crankcase oil are not fully understood. However, it is believed that the combination of ingredients comprising the reagents referred to above, which, in the case of the acids, are preferably but not necessarily premixed in relation to the time of addition to the waste crankcase oil, is effective to separate contaminants which heretofore apparently completely resisted efforts at separation thereof intact or without undesirable acid sludgeforming, when other prior known reagents were added to the waste oil product.

The role of the dimethyl sulfoxide or dimethyl formamide reagents is likewise not understood with certainty, but it is considered possible that these reagents may be effective in displacing air from the complex colloidal system by which contaminants are held in suspension and dispersed in the oil. It is thought that adsorbed air may give the complex sol virtually the exact density as the body of the oil of which it is a part, thereby creating a dispersion or suspension which resists breakage by physical methods, such as centrifuging. Liberating adsorbed air from dispersed particles may raise the density thereof so that settling under the influence of gravity is made possible. In this connection, the solvents seem to be an antidetergent, which helps disrupt the equilibrium attained by the detergent-oil'suspended particle system.

As pointed out above, the present invention is highly effective when used on waste crankcase oil, particularly the waste crankcase oil which has been partially re-refined in the manner referred to and incorporated by reference herein from my copending application. However, other crankcase oil products may be treated as set forth herein with success, provided that partial re-refining treatment thereof has not been under such harsh conditions that the composition of the additives therein has been significantly affected. In particular, another highly important advantage of the invention is that it provides a method which makes re-refming of waste crankcase oil possible without creating undesirable acid sludge, which is dangerous, and difficult and expensive to dispose of, and still harmful to nature when disposed of in any presently known manner.

it will thus be seen, by reference to the foregoing description and the appended claims, that the present invention provides a novel re-refining crankcase oil, a novel additive mixture separated therefrom, and method of making such product, having numerous advantages and characteristics, including those previously pointed out and others which are inherent in the invention.

lclaim:

1. A method of removing contaminants suspended in substantially dewatered waste crankcase oil, including detergents and other additives adapted to suspend such contaminants in said crankcase oil, said contaminants including metallic iron, iron-containing compounds, and other nonhydrocarbon containing contaminants, said method comprising treating said waste crankcase oil with from about 0.1 percent to about 2 percent by volume of a treating composition including a nitrate ionkcontaining compound and sulfuric acid, said nitrate ion being present in a relation of from about one-half part by weight to about two parts by weight for each part by weight of sulfuric acid, agitating said waste oil and said treating composition to effect thorough mixing thereof, allowing the contaminants in said oil to settle and drawing off the substantially contaminant-free oil thus treated from above said settled contaminants without substantial regeneration of any of said detergents or additives.

2. A method as defined in claim 1 in which said mixture to be treated by said treating composition of pretreated by addition thereto of from about 0.005 percent to about 10 percent by weight of a treating compound selected from the class consisting of compounds which generate free hydroxyl radicals and metal halide compounds, and with from about 0.005 percent to about 10 percent by weight of a strong electrolyte in a concentrated electrolytic solution, followed by separation of the thus pretreated and partly refined oil from the remainder of the oil containing contaminants thus separated.

3. A method as defined in claim 1 which further includes additionally treating said oil to which said treating composition has been added, with a substantially equal volume of a compound from the class consisting of dimethyl formamide and dimethyl sulfoxide.

4. A method as defined in claim 1 which further includes additionally treating said oil to which said treating composition has been added, with a substantially equal volume of dimethyl formamide.

5. A method as defined in claim 1 which further includes additionally treating said oil to which said treating composition has been added, with a substantially equal volume of dimethyl sulfoxide.

6. A method as defined in claim 1 in which said nitrate ioncontaining compound is nitric acid.

7. A method as defined in claim I in which said nitrate ioncontaining compound is nitric acid, and in which said nitric acid and said sulfuric acid are mixed with each other prior to being added to said waste crankcase oil.

8. A method as defined in claim 2 in which said nitrate ioncontaining compound is nitric acid, and in which said nitric acid and said sulfuric acid are mixed with each other prior to being added to said waste crankcase oil.

9. A method as defined in claim 1 in which said oil is a partly refined waste crankcase oil having less than 1 percent water, being substantially free of impurities other than additives originally present in said oil material suspended in said oil by said additives, and reaction products of said additives.

10. A method as defined in claim 1 which further includes, following the step of adding said treating composition, heating said oil to a temperature of from about 50 C. to about C.

11. A method as defined in claim 1 which includes, prior to said step of allowing separation of said additives, subjecting said oil and said treating composition to a high shear mixing action while said treating composition is in contact with said oils.

12. A method as defined in claim 1 which further includes adding a detergent to the treating solution, said additional detergent being present in an amount less than 0.05 percent by weight in relation to the weight of the composition furnishing nitrate ions.

22%;? UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 7,731 Dated September 21 1971 Invenwfl Graham L. Qulick It is certified that error. appears in the above-identified patent; and that: said Letters Patent are hereby corrected as shown below:

r- Column 4, line .7, cancel "considerably" and insert -considerable-- Column 6, line 3, cancel "an'" and insert --and- Column 6, line 63, cancel "re-refining" and insert -re-ref"1ned- Column 7, line 2, Cancel "ionkcontaining" and insert --ioncontaining-- ifilolumn 7, line 12, cancel "of" and insert --is-- Column 8, line 27, after adding delete "a" and insert --an additional-- Column 8, line 27, after "said" delete "additional" i ned and sealed this 25th day of March 1 972.

'(saAL) Attest:

ROBERT GOTTS'CHALK EDWARD M.FLETCHER, Commissioner of Patents Attesting Officer 

2. A method as defined in claim 1 in which said mixture to be treated by said treating composition of pretreated by addition thereto of from about 0.005 percent to about 10 percent by weight of a treating compound selected from the class consisting of compounds which generate free hydroxyl radicals and metal halide compounds, and with from about 0.005 percent to about 10 percent by weight of a strong electrolyte in a concentrated electrolytic solution, followed by separation of the thus pretreated and partly refined oil from the remainder of the oil containing contaminants thus separated.
 3. A method as defined in claim 1 which further includes additionally treating said oil to which said treating composition has been added, with a substantially equal volume of a compound from the class consisting of dimethyl formamide and dimethyl sulfoxide.
 4. A method as defined in claim 1 which further includes additionally treating said oil to which said treating composition has been added, with a substantially equal volume of dimethyl formamide.
 5. A method as defined in claim 1 which further includes additionally treating said oil to which said treating composition has been added, with a substantially equal volume of dimethyl sulfoxide.
 6. A method as defined in claim 1 in which said nitrate ion-containing compound is nitric acid.
 7. A method as defined in claim 1 in which said nitrate ion-containing compound is nitric acid, and in which said nitric acid and said sulfuric acid are mixed with each other prior to being added to said waste crankcase oil.
 8. A method as defined in claim 2 in which said nitrate ion-containing compound is nitric acid, and in which said nitric acid and said sulfuric acId are mixed with each other prior to being added to said waste crankcase oil.
 9. A method as defined in claim 1 in which said oil is a partly refined waste crankcase oil having less than 1 percent water, being substantially free of impurities other than additives originally present in said oil material suspended in said oil by said additives, and reaction products of said additives.
 10. A method as defined in claim 1 which further includes, following the step of adding said treating composition, heating said oil to a temperature of from about 50* C. to about 90* C.
 11. A method as defined in claim 1 which includes, prior to said step of allowing separation of said additives, subjecting said oil and said treating composition to a high shear mixing action while said treating composition is in contact with said oils.
 12. A method as defined in claim 1 which further includes adding a detergent to the treating solution, said additional detergent being present in an amount less than 0.05 percent by weight in relation to the weight of the composition furnishing nitrate ions. 